ANIMAL GRAFTS AND REGENERATIONS. 239 
comes unfit for ossification. Robin and Dubreuil have also 
proved that bony tissue may be formed without any carti- 
lage existing beforehand, without any intervention of mem- 
brane, and may proceed directly from a bone deprived of 
membrane. These discoveries, without taking from the peri- 
osteum the evident share which it has in producing renova- 
tions of bone, give a conception of its mechanical action 
which differs from that which physiologists had admitted. 
They prove that really, in experiments of the kind tried by 
Duhamel, Heine, Flourens, it is bone which produces bone, 
as the severed nerve produces nerve. The cartilaginous 
or bony layer adhering to the periosteum is in fact noth- 
ing else than bone in process of formation; and whenever, 
whether by means of the periosteum or by means of an 
irritation, the reproduction of a certain quantity of bone 
is procured, it is because, in the first place, conditions fit 
for the production of cartilage have been brought about. 
These remarks will allow us to understand and to give a 
rapid estimate of the value of surgical methods founded on 
the knowledge of these facts. 
Diseases of the bones are numerous. Independently 
of those cases in which they are directly injured by pro- 
jectiles, they are liable to inflammations, tumors, and decay 
of every kind. These diseases are slow, in proportion to 
the slowness of vital elaborations in those organs, but they 
are not the less destructive, and they always end by bring- 
ing about a more or less considerable corruption of the 
substance of the bones. It is then necessary that the mat- 
ters given off by the diseased bone should be cleared away: 
the mortified portions must be got rid of. The limb very 
soon swells, and becomes painful. Pieces make their way 
through the skin, suppurations are set up, and, if art does 
not interfere, the patient is led by exhaustion to a miser- 
able death. To this concourse of evils surgery opposes 
difficult operations. It cuts deep openings, it loosens the 
